Deposition of discrete nanoparticles on an implant surface

ABSTRACT

A method of forming a nanocrystalline surface on an implant is disclosed. The method comprises the act of roughening at least a portion of the implant surface to form a roughened surface. The method further comprises the act of, without forming an alkoxide on the roughened surface, depositing nanocrystals on the roughened surface. The nanocrystals comprise a material having a property that promotes osseointegration.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/736,269, filed Nov. 14, 2005, and U.S. Provisional Application No.60/797,810, filed May 4, 2006, both of which are incorporated byreference in their entireties.

FIELD OF THE INVENTION

This invention relates generally to implants and, in particular, to adental implant having discrete nanocrystalline calcium phosphateparticles deposited thereon and methods of making the same.

BACKGROUND OF THE INVENTION

It is becoming more common to replace a missing tooth with a prosthetictooth that is placed upon and attached to a dental implant. Dentalimplants are often comprised of metal and metal alloys, includingtitanium (Ti) and titanium alloys. The dental implant serves as anartificial root that integrates with the gingiva and the bone tissue ofthe mouth.

For the dental implant to function successfully, sufficientosseointegration is required. In other words, a direct chemical bondbetween the implant and the bone must be formed and retained.Osseointegration materials may be incorporated onto the surface of theimplant to help enhance the osseointegration process. Non-limitingexamples of osseointegration materials include calcium phosphate ceramicmaterials such as hydroxyapatite (HA), which is particularly chemicallystable and osseoconductive.

To provide sufficient long-term behavior of an implant having anosseointegration compound on the surface, there must be a sufficientbond strength between the implant and the compound. Moreover, thecompound is desirably sufficiently biostable such that the rate ofdissolution of the compound is low.

Several existing techniques involve forming a generally thin (e.g.,generally less than 10 microns) coating of HA, other calcium phosphates,or other osseointegration compounds for improving the bond strength ofthe coating to the implant. Plasma spraying and sputtering are two majortechniques that have been used to deposit, for example, HA onto animplant. The dissolution rate of HA for these processes, however, may beundesirably high. Moreover, the interface of the HA and the implant isprone to fracture, which is often caused by poor adherence of the HA tothe metal implant.

U.S. Pat. App. Pub. No. 2004/0249472 discloses a method of coating animplant with nanoscale calcium phosphate (e.g., HA). Although effective,the disclosed process is hazardous in that it requires utilizing highlyflammable chemicals and produces hazardous byproducts (e.g., waste).Moreover, the process is inefficient because it requires that theimplant first be coated with a layer comprising alkoxides ortri-functional silanes (i.e., aminopropyltriethoxysilane) to form apositively charged surface of the implant. A second coating layercomprising negatively charged HA nanoparticles is then formed on thefirst coating layer.

The present invention is directed to an improved implant having discretenanocrystalline calcium phosphate (e.g., HA) deposited on the implantsurface and methods of forming the same.

SUMMARY OF THE INVENTION

The present invention relates to a method of forming a nanocrystallinesurface on an implant. The method comprises the act of roughening atleast a portion of the implant surface to form a roughened surface. Themethod further comprises the act of, without forming an alkoxide on theroughened surface, depositing nanocrystals on the roughened surface. Thenanocrystals comprise a material having a property that promotesosseointegration.

According to another embodiment of the present invention, a dentalimplant is disclosed. The dental implant comprises a head portion havinga non-rotational feature. The dental implant further comprises alowermost end opposing the head portion. The dental implant furthercomprises a threaded bottom portion for engaging bone between the headportion and the lowermost end. The threaded bottom portion has aroughened surface with a substantially uniform array of irregularitieshaving peak-to-valley heights not greater than about 20 microns. Thethreaded bottom portion further includes discrete nanoparticles locatedon the roughened surface. The nanoparticles include hydroxyapatitenanocrystals.

According to another embodiment of the present invention, a method offorming a nanocrystalline surface on an implant is disclosed. The methodcomprises the act of providing a metal substrate. The method furthercomprises the act of immersing at least a portion of the substrate in acolloidal solution having a temperature ranging from about 18° C. toabout 32° C. for about 11.5 minutes to about 240 minutes. The colloidalsolution comprises a 2-methoxyethanol solvent and a plurality ofhydroxyapatite nanocrystals having a concentration ranging from about0.01 weight percent to about 1 weight percent relative to the overallsolution. The method further comprises adjusting the pH of the colloidalsolution to about 9 to about 11.

The above summary of the present invention is not intended to representeach embodiment, or every aspect, of the present invention. This is thepurpose of the figures and the detailed description which follow.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other advantages of the invention will become apparentupon reading the following detailed description and upon reference tothe drawings.

FIG. 1 is a side view of an implant according to one embodiment.

FIGS. 2 a, 2 b, and 2 c, are a side view, an insertion end view, and agingival end view, respectively, of an implant according to a secondembodiment.

FIGS. 3 a, 3 b, and 3 c, are a side view, an insertion end view, and agingival end view, respectively, of an implant according to a thirdembodiment.

FIGS. 4 a and 4 b are a side view, an end view, and a cross-sectionalview, respectively, of an implant according to a fourth embodiment.

FIG. 5 is a flow diagram detailing a method of forming an implantaccording to an embodiment of the present invention.

FIG. 6 is a side view of the implant of FIG. 1 with a roughened outersurface.

FIG. 7 a is a flow diagram detailing a method of forming an implantaccording to another embodiment of the present invention.

FIG. 7 b is a flow diagram detailing a method of forming an implantaccording to yet another embodiment of the present invention.

FIG. 8 a is a field emission scanning electron microscope (FESEM) imageshowing hydroxyapatite nanoparticles at 10 kX.

FIG. 8 b is an FESEM image showing hydroxyapatite nanoparticles at 30kX.

FIGS. 9-13 are FESEM images showing hydroxyapatite nanoparticles at 30kX deposited onto an implant surface using various methods of thepresent invention.

DETAILED DESCRIPTION

The present invention is directed to implants having discretenanocrystalline calcium phosphate particles deposited thereon andmethods of making the same. An implant in the context of the presentinvention means a device intended to be placed within a human body suchas to connect skeletal structures (e.g., a hip implant) or to serve as afixture for a body part (e.g., a fixture for an artificial tooth).Although the remainder of this application is directed to a dentalimplant, it is contemplated that the present invention may also beapplied to other (e.g., medical) implants.

FIG. 1 shows a standard dental implant 10 that includes an head portion12, a lowermost end 14, and a threaded bottom portion 16. The implant 10may, for example, be made of titanium, tantalum, cobalt, chromium,stainless steel, or alloys thereof. It is contemplated that othermaterials such as ceramics or ceramic-titanium combinations may also beused. FIGS. 2 a-c, 3 a-c, and 4 a-b, which are discussed below, describealternative implant designs that may also be used with the presentinvention.

In the implant 10 of FIG. 1, the head portion 12 includes anon-rotational feature. In the embodiment shown, the non-rotationalfeature includes a polygonal boss 20 that may be engageable with a toolthat screws the implant 10 into bone tissue. In the illustratedembodiment, the polygonal boss 20 is hexagonal. The polygonal boss 20may also be used for non-rotationally engaging a correspondingly shapedsocket on a restorative or prosthetic component that is attached to theimplant 10.

The exterior of the threaded bottom portion 16 facilitates bonding withbone or gingiva. The threaded bottom section 16 includes a thread 18that makes a plurality of turns around the implant 10. The threadedbottom portion 16 may further include a self-tapping region withincremental cutting edges 17 that allows the implant 10 to be installedwithout the need for a bone tap. These incremental cutting edges 17 aredescribed in detail in U.S. Pat. No. 5,727,943, entitled “Self-Tapping,Screw-Type Dental Implant,” which is incorporated by reference in itsentirety.

FIGS. 2 a-c disclose an implant 36 that differs from the implant 10 ofFIG. 1 in the details of the cutting edges 17′ and the contours of thethreads defining the exterior of the threaded bottom portion 16′. Whenviewed in the cross-section (see FIG. 1 b), the threaded outer surface16′ is non-circular in the region of the threads and/or the troughsbetween the threads. This type of thread structure is described indetail in U.S. Pat. No. 5,902,109, entitled “Reduced Friction,Screw-Type Dental Implant,” which is incorporated by reference in itsentirety.

In FIGS. 3 a-c, an implant 41 having a wide diameter in the region ofthe threaded bottom portion 42 is illustrated. The diameter is in therange of from about 4.5 mm to about 6.0 mm with the diameter of 5.0 mmbeing a fairly common dimension for a wide diameter implant. Such animplant 41 is useful to engage one or both cortical bones to provideenhanced stability, especially during the period of time afterinstallation.

FIGS. 4 a-b illustrate an implant 110 according to another embodimentthat may be used with the present invention. The implant 110 includes amiddle section 114 designed to extend through the gingiva. Preferably,it is a smooth surface that includes a titanium nitride coating so theunderlying titanium or titanium alloy is not readily seen through thegingiva. The implant 110 also includes a threaded portion 120 that mayinclude various thread structures and is preferably roughened toincrease the osseointegration process. It is contemplated that implantsother than those illustrated in FIGS. 1-4 may be used with the presentinvention.

According to the present invention, a nanoparticle deposition overliesat least a portion (e.g., the threaded bottom portion) of the surface ofan implant. In one embodiment, the nanoparticle deposition is a materialthat promotes osseointegration between the implant and bone material(e.g., human bone material). One suitable material is a calciumphosphate material, such as hydroxyapatite (HA). In one embodiment, thenanoparticle deposition includes HA nanocrystals having dimensionsranging from about 10 nanometers to about 150 nanometers. In anotherembodiment, the HA nanocrystals have dimensions ranging from about 20nanometers to about 100 nanometers.

Turning now to FIG. 5, a general method of depositing nanoparticles ofcalcium phosphate onto the surface of an implant is set forth accordingto one embodiment of the present invention. At step s200, an implant isprovided. At least a portion of the implant surface is roughened at steps201. As an example, FIG. 6 shows the implant 10 of FIG. 1 having aroughened surface 130. Discrete nanoparticles comprising a materialhaving a property that promotes osseointegration are then deposited ontothe roughened surface of the implant at step s202.

Referring now to FIG. 7 a, another general method of forming an implantaccording to another embodiment of the present invention is illustrated.An implant comprised of titanium, a titanium alloy (e.g., titanium6AL-4V ELI alloy), stainless steel, ceramic, or the like is provided atstep s250. At step s254, discrete nanoparticles comprising a materialhaving a property that promotes osseointegration (e.g., HA nanocrystals)are then deposited onto the roughened surface of the implant. Theimplant may then be rinsed in reverse osmosis/deionized (RO/DI) water toremove residual solvents and HA at step s258. The implant is then driedat step s264.

Referring to FIG. 7 b, a more detailed method of depositing HAnanocrystals onto the surface of a dental implant is illustratedaccording to another embodiment of the present invention. A threadeddental implant comprised of titanium, a titanium alloy (e.g., titanium6AL-4V ELI alloy), stainless steel, or the like is provided at steps300. The surface of the dental implant is generally clean and dry. Athreaded bottom portion of the implant is etched to remove a nativeoxide layer from the implant surface at step s301. The native oxidelayer may be removed by a first acid solution, which may include aqueoushydrofluoric acid. The threaded bottom portion is then acid etched toform a roughened surface at step s302. The acid etching step may includea mixture of sulfuric and hydrochloric acids. The roughened surfaceforms a substantially uniform array of microscale irregularities forenhancing the integration of the implant with bone or other biologicalinterfaces. “Microscale,” as used herein, should be understood todescribe an article or feature generally measured in microns such as,for example, 1 micron to 100 microns. The irregularities may includemicroscale cone-shaped elements and generally have peak-to-valleyheights not greater than about 20 microns and are preferably about 1micron to about 10 microns. This type of roughening method utilized oncommercially pure (CP) titanium is described in detail in U.S. Pat. No.5,876,453 entitled “Implant Surface Preparation,” which is incorporatedby reference in its entirety. An additional roughening method utilizedon Titanium 6AL-4V ELI alloy is described in detail in U.S. Pat. App.Pub. No. 2004/0265780 entitled “Surface Treatment Process for ImplantsMade of Titanium Alloy,” which is also incorporated by reference in itsentirety. It is contemplated that other surface roughening techniquesincluding, but not limited to, grit blasting and titanium plasma spraymay be used. After these acid-etching steps, the implant may then berinsed in hot deionized water (e.g., 70° C. to 100° C.) to remove anyacid residuals and to potentially enhance titanium hydroxide groups onthe surface at step s304.

The HA nanocrystals are then deposited onto the roughened surface of theimplant at step s306. The HA nanocrystals may be introduced onto theroughened surface of the implant in the form of a colloid. Arepresentative amount of HA in the colloid is typically in the range ofabout 0.01 weight percent to about 1 weight percent (e.g., 0.10 weightpercent). To form the colloid, HA nanocrystals may be combined insolution with a 2-methoxyethanol solvent and ultrasonically dispersedand deagglomerated. The pH of the colloidal solution may be adjustedwith sodium hydroxide, ammonium hydroxide, or the like on the order ofabout 7 to about 13. As such, the colloidal solution may include HAnanocrystals, 2-methoxyethanol, and a pH adjuster (e.g., ammoniumhydroxide, and/or sodium hydroxide).

In preparing a solution of HA nanocrystals, raw HA nanocrystal materialmay be refined to achieve a stock solution with limited agglomeration ofcrystals. According to one method, BABI-HAP-N20-E HA material,manufactured by Berkley Advanced Biomaterials (Berkley, Calif.), isdried to form a cake. The cake is then mechanically crushed into a finepowder and subsequently combined with a 2-methoxyethanol solution. Thesolution is then ultrasonically dispersed to deagglomerate the HAnanocrystals. The solution is then allowed to settle and is decanted. Atop portion of the settled solution is used as a stock solution formanufacturing a deposition solution. The stock solution is tested toconfirm particle size distribution and HA concentration. An appropriateparticle size distribution (volume) as indicated by the Nanotrac 150(Microtrac, Inc., North Largo, Fla.) has a D10 (tenth percentiledistribution) of less than 150 nanometers, a D50 (fiftieth percentiledistribution) of less than 300 nanometers, and a D90 (ninetiethpercentile distribution)) of less than 900 nanometers.

The deposition solution is prepared by combining the stock solution ofappropriately sized HA nanocrystals in 2-methoxyethanol with additional2-methoxyethanol to achieve a desired concentration. One suchconcentration ranges from about 0.08 weight percent to about 0.12 weightpercent HA in 2-methoxyethanol. It is contemplated that theconcentration of HA may be lower than 0.08 weight percent or higher than0.12 weight percent, provided that other variables (e.g., immersion timeand pH) are modified accordingly.

The deposition solution may be pH adjusted with, for example, ammoniumhydroxide. More basic solutions generally accelerate the depositionprocess and allow larger particles to be deposited on the implantsurface. Suitable concentrations may range from between about 0.05weight percent to about 0.1 weight percent ammonium hydroxide. A 25% byweight combination of the pH adjusted deposition solution with deionizedwater generally has a pH of about 9 to about 11.

The HA nanocrystals are then deposited on the surface of the implant by,for example, dipping the implant into the colloidal solution. Thesolution may be mixed initially but is generally stagnant duringdeposition. The implant may, for example, be immersed in the colloidalsolution for several hours (e.g., 2 hours to 4 hours). The depositionmay be performed at generally ambient temperatures or at temperatureshigher or lower than ambient temperature. The HA nanocrystals bonddirectly to the titanium hydroxide and/or titanium oxide.

Immersion time and HA concentration are among several factors thataffect the rate and amount of deposition of HA nanocrystals onto theimplant surface. Immersing the implant in a solution having aconcentration of about 0.1 weight percent HA and a pH of approximately10 for about 60 minutes, for example, typically results in depositioncovering about 40% to about 60% of the implant surface. Longer immersiontimes generally provide greater coverage and may form a layer or coatingon the implant surface. Conversely, shorter immersion times generallydecrease the amount of material deposited on the implant surface.Solutions having lower concentrations of HA nanocrystals generallyrequire longer immersion times, whereas solutions having higherconcentrations of HA nanocrystals generally require shorter immersiontimes.

Another factor affecting the rate and amount of deposition of HAnanocrystals onto the implant surface is the pH of the depositionsolution. The pH of the solution also affects, to some degree, the sizeof the HA nanocrystals that are deposited on the implant. At an acidicpH (i.e., less than 7), the deposition rate is generally slow, and theaverage size of the particles deposited onto the implant surfacegenerally decreases. At a neutral pH (approximately 7), the depositionoccurs relatively slowly. For example, if a deposition solution havingan HA concentration of about 0.1 weight percent is used, the implantmust be immersed for about 2 hours to about 4 hours to achieve about 40%to about 60% coverage. Additionally, the particles deposited on thesurface are generally smaller (about 20 nanometers) and more uniform. Atan elevated pH (i.e., greater than 9), the size of the HA nanocrystalsdeposited is generally greater, ranging from about 20 nanometers toabout 150 nanometers. The process time for a solution having an HAconcentration of about 0.1 weight percent and a pH greater than about 9is also generally shorter, with an immersion time of 60 minutesresulting in deposition coverage of about 40% to about 60%.

The implant may then be rinsed in reverse osmosis/deionized (RO/DI)water to remove residual solvent and HA at step s308. The implant isthen dried (e.g., oven dried). At optional step s310, the implant maythen be thermally cured to sinter the HA at a temperature ranging fromapproximately 80° C. to approximately 500° C. (e.g., about 100° C.).

Additional acts may then be performed to correct potential aestheticdiscoloration of the implants that may occur during the method ofdepositing the HA nanocrystals on the implant. For example, at steps312, the implant is rinsed in deionized water at a temperature rangingfrom approximately 40° C. to approximately 80° C. to remove any waterspotting that may have formed on the implant. The implant may then bedried. The implant may, for example, be oven dried at a temperatureranging from approximately 80° C. to approximately 500° C. at step s314.

The implant surface may be characterized utilizing Field EmissionScanning Electron microscopy (FESEM). Depending upon the resolution ofthe instrument, the deposition of the nanoparticles may typically bewitnessed at magnifications of over 10 kX (e.g., 30 kX). The amount ofdiscrete nanocrystalline deposition coverage may be analyzed byconducting contrast phase analysis on FESEM images using computersoftware. The adhesion of nanocrystals to the surface of an implant maybe verified through functional testing or novel techniques such astesting adhesion strength (e.g., shear strength) using atomic forcemicroscopy and a nanometer length scale silica nitride (SiN) calibratedbeam with a diamond coated probe or tip.

According to another method of the present invention, discretenanoparticles (e.g., HA nanocrystals) are deposited onto an implantsurface without first roughening the surface of the implant. In thisembodiment, the implant is machined, and its final surface configurationis generally smooth as compared to the acid-etching steps previouslydescribed.

The colloidal solutions referred to in Examples 1-10 below were preparedusing the processes previously set forth above. After the HA nanocystalswere deposited on the implant surface in Examples 1-10, the implantswere oven dried at a temperature of approximately 100° C.

EXAMPLE 1

FIGS. 8 a, 8 b are scanning electron microscope images showing HAnanocrystals 402 after being deposited on the surface of a CP titaniumimplant 400. The image of FIG. 8 a was taken at 10 kX utilizing anFESEM. The image of FIG. 8 b was taken at 30 kX utilizing an FESEM.

The surface of the implant 400 shown in FIGS. 8 a, 8 b was roughenedusing a citric acid etching process, described in U.S. patentapplication Ser. No. 11/361,286, which has been incorporated byreference herein, to produce an Osseotite® surface. The rougheningprocess resulted in irregularities 404 having peak-to-valley heights ofno more than 10 microns. The HA nanocrystals 402 were deposited on thesurface of the implant 400 using a colloidal solution. The colloidalsolution included about 0.07 weight percent of HA in a 2-methoxyethanolsolvent. The implant 400 was immersed in the colloidal solution forapproximately 4 hours. The resulting deposition of HA nanocrystals 402on the implant 400 are shown in FIGS. 8 a, 8 b.

EXAMPLE 2

FIG. 9 a is a scanning electron microscope image showing HA nanocrystals502 after being deposited on the surface of an implant 500. The image ofFIG. 9 a was taken at 30 kX utilizing an FESEM.

The implant 500 used in FIG. 9 a was comprised of titanium 6AL-4V ELIalloy. The surface of the implant 500 shown in FIG. 9 a was roughenedusing the dual acid-etched process described in U.S. Pat. App. Pub. No.2004/0265780, which has been incorporated by reference herein. The HAnanocrystals 502 were deposited on the surface of the implant 500 usinga colloidal solution described above including about 0.10 weight percentof HA in a 2-methoxyethanol solvent. The implant 500 was immersed in thecolloidal solution for approximately 150 minutes at ambient temperature.The resulting deposition of HA nanocrystals 502 on the implant 500 isshown in FIG. 9 a.

EXAMPLE 3

FIG. 9 b is a scanning electron microscope image showing HA nanocrystals552 after being deposited on the surface of a titanium 6AL-4V ELI alloyimplant 550. The image of FIG. 9 b was taken at 30 kX utilizing anFESEM.

The procedure used for depositing the HA nanocrystals 552 on the surfaceof the implant 550 was generally similar to the procedure used inExample 2. However, unlike the procedure of Example 2, the pH of thecolloidal solution of Example 3 was adjusted with ammonium hydroxide to0.10 weight percent ammonium hydroxide. The pH of the adjusted solutionwas between 9 and 10 when measured at about 25 weight percent indeionized H₂O. The implant 550 was immersed in the colloidal solutionfor approximately 60 minutes at ambient temperature. The resultingdeposition of HA nanocrystals 552 on the implant 550 is shown in FIG. 9b.

As shown in FIG. 9 b, deposition of HA nanocrystals 552 on the surfaceof the implant 550 is comparable to that of the implant 500 of FIG. 9 a.However, the immersion time of the implant 550 was considerably shorter.Thus, adjusting the pH to form a more basic solution was shown toshorten the process time required for deposition of the HA nanocrystals552 on the surface of the implant.

EXAMPLE 4

FIG. 9 c is a scanning electron microscope image showing HA nanocrystals602 after being deposited on the surface of a titanium 6AL-4V ELI alloyimplant 600. The image of FIG. 9 c was taken at 30 kX utilizing anFESEM.

The procedure used for depositing the HA nanocrystals 602 on the surfaceof the implant 600 was similar to the procedure used in Example 3.However, unlike the implant 550 of Example 3, the surface of the implant600 shown in FIG. 9 c was not roughened. Rather, the surface of theimplant 600 was machined, and its final surface configuration prior todepositing the HA nanocrystals 602 was generally smooth.

As shown in FIG. 9 c, the deposition of HA nanocrystals 602 on thesurface of the implant 600 is comparable to that of the implants 500,550 of FIGS. 9 a and 9 b respectively. Thus, adequate deposition of HAnanocrystals on an implant surface may occur without roughening theimplant surface prior to deposition.

EXAMPLE 5

FIG. 9 d is a scanning electron microscope image showing HA nanocrystals652 after being deposited on the surface of an implant 650. The image ofFIG. 9 d was taken at 30 kX utilizing an FESEM.

The procedure used for depositing the HA nanocrystals 652 on the surfaceof the implant 650 was similar to the procedure used in Example 3.However, the implant 650 used in FIG. 9 d was comprised of 316 stainlesssteel such that it could be used on, for example, a cortical screw. Thesurface of the substrate was not roughened prior to deposition. Theimplant 650 was immersed in the colloidal solution for approximately 120minutes at ambient temperature. The resulting deposition of HAnanocrystals 652 on the implant 650 is shown in FIG. 9 d.

As shown in FIG. 9 d, the amount of HA nanocrystals 652 deposited on thesurface of the implant 650 is comparable to that of FIGS. 9 a-c. Thus,adequate deposition of HA nanocrystals on an implant surface may occuron implants comprising metals other than titanium and titanium alloys(e.g., stainless steel).

EXAMPLE 6

FIG. 10 is a scanning electron microscope image showing HA nanocrystals702 after being deposited on the surface of an implant 700. The image ofFIG. 10 was taken at 30 kX utilizing an FESEM.

The implant 700 used in FIG. 10 was comprised of titanium 6AL-4V ELIalloy. The surface of the implant 700 shown in FIG. 10 was roughenedusing the dual acid-etched process described in U.S. Pat. App. Pub. No.2004/0265780, which has been incorporated by reference herein. The HAnanocrystals 702 were deposited on the surface of the implant 700 usinga colloidal solution including about 0.80 weight percent of HA in a2-methoxyethanol solvent. The pH of the colloidal solution was adjustedwith ammonium hydroxide to 0.01 weight percent ammonium hydroxide. ThepH of the adjusted solution was between 8 and 9 when measured at about25 weight percent in deionized H₂O. The implant 700 was immersed in thecolloidal solution for approximately 55 minutes at a temperature ofabout 18° C. The resulting deposition of HA nanocrystals 702 on theimplant 700 is shown in FIG. 10.

The procedure of Example 6 utilized a lower concentration of HAnanocrystals (i.e., 0.08 weight percent) and a relatively lowconcentration of ammonium hydroxide (i.e., 0.01 weight percent). Thedeposition of HA nanocrystals 702 on the surface of the implant 700,however, is comparable to that of FIGS. 9 a-d.

EXAMPLE 7

FIG. 11 is a scanning electron microscope image showing HA nanocrystals752 after being deposited on the surface of an implant 750. The image ofFIG. 11 was taken at 30 kX utilizing an FESEM.

The implant 750 used in FIG. 11 was comprised of titanium 6AL-4V ELIalloy. The surface of the implant 750 shown in FIG. 11 was roughenedusing the dual acid-etched process described in U.S. Pat. App. Pub. No.2004/0265780, which has been incorporated by reference herein. The HAnanocrystals 752 were deposited on the surface of the implant 750 usinga colloidal solution including about 0.12 weight percent of HA in a2-methoxyethanol solvent. The pH of the colloidal solution was adjustedwith ammonium hydroxide to 0.30 weight percent ammonium hydroxide. ThepH of the adjusted solution was between 10 and 11 when measured at about25 weight percent in deionized H₂O. The implant 550 was immersed in thecolloidal solution for approximately 70 minutes at a temperature ofabout 30° C. The resulting deposition of HA nanocrystals 752 on theimplant 750 is shown in FIG. 11.

The procedure of Example 7 utilized a higher concentration of HAnanocrystals (i.e., 0.12 weight percent) than that of Example 6 (i.e.,0.08 weight percent). The procedure of Example 7 also substantiallyincreased the concentration of ammonium hydroxide (i.e., 0.30 weightpercent) as compared to the procedure of Example 6. The deposition of HAnanocrystals 752 on the surface of the implant 750, however, iscomparable to those of the examples above.

EXAMPLE 8

FIG. 12 a is a scanning electron microscope image showing HAnanocrystals 780 after being deposited on the surface of an implant 775.The image of FIG. 12 a was taken at 30 kX utilizing an FESEM.

The implant 775 used in FIG. 12 a was comprised of CP titanium. Thesurface of the implant 775 shown in FIG. 12 a was roughened using thedual acid-etched process described in U.S. Pat. No. 5,876,453, which hasbeen incorporated by reference herein. The HA nanocrystals 780 weredeposited on the surface of the implant 775 using a colloidal solutionincluding about 0.1 weight percent of HA in a 2-methoxyethanol solvent.The pH of the colloidal solution was adjusted with ammonium hydroxide to0.05 weight percent ammonium hydroxide. The pH of the adjusted solutionwas between 9 and 10 when measured at about 25 weight percent indeionized H₂O. The implant 775 was immersed in the colloidal solutionfor approximately 11.5 minutes at ambient temperature. The immersiontime, 11.5 minutes, is relatively low compared to that of the previousexamples. Accordingly, the amount of HA nanocrystals 780 deposited onthe surface of the implant 775 is generally less than those of theprevious examples.

EXAMPLE 9

FIG. 12 b is a scanning electron microscope image showing HAnanocrystals 802 after being deposited on the surface of a CP titaniumimplant 800. The image of FIG. 12 b was taken at 30 kX utilizing anFESEM.

The procedure used for depositing the HA nanocrystals 802 on the surfaceof the implant 800 was similar to the procedure used in Example 8.However, the immersion time used in FIG. 12 b was approximately 60minutes. Thus, the immersion time is higher than that of Example 8.Accordingly, the amount of HA nanocrystals 802 deposited on the surfaceof the implant 800 is generally greater than that of Example 8.

EXAMPLE 10

FIG. 12 c is a scanning electron microscope image showing HAnanocrystals 830 after being deposited on the surface of a CP titaniumimplant 825. The image of FIG. 12 c was taken at 30 kX utilizing anFESEM.

The procedure used for depositing the HA nanocrystals 830 on the surfaceof the implant 825 was similar to the procedure used in Examples 8 and9. However, the immersion time used in FIG. 12 c was approximately 240minutes. Thus, the immersion time is considerably higher than those ofExamples 8 and 9. Accordingly, the amount of HA nanocrystals 830deposited on the surface of the implant 825 is generally greater thanthose of Examples 8 and 9.

EXAMPLE 11

FIG. 13 a is a scanning electron microscope image showing HAnanocrystals 852 after being deposited on the surface of an implant 850.The image of FIG. 13 a was taken at 30 kX utilizing an FESEM.

The implant 850 used in FIG. 13 a was comprised of titanium 6AL-4V ELI.The surface of the implant 850 shown in FIG. 13 a was roughened usingthe dual acid-etched process described in U.S. Pat. App. Pub. No.2004/0265780, which has been incorporated by reference herein. The HAnanocrystals 852 were deposited on the surface of the implant 850 usinga colloidal solution including about 0.10 weight percent of HA in a2-methoxyethanol solvent. The pH of the colloidal solution was adjustedwith ammonium hydroxide to 0.05 weight percent ammonium hydroxide. Theimplant 850 was immersed in the colloidal solution for approximately11.5 minutes at ambient temperature.

The resulting deposition of HA nanocrystals 852 on the implant 850 isshown in FIG. 13 a. The immersion time, 11.5 minutes, is relatively lowcompared to that of the previous examples. Accordingly, the amount of HAnanocrystals 852 deposited on the surface of the implant 850 isgenerally less than those of the previous examples.

EXAMPLE 12

FIG. 13 b is a scanning electron microscope image showing HAnanocrystals 880 after being deposited on the surface of a titanium6AL-4V ELI alloy implant 875. The image of FIG. 13 b was taken at 30 kXutilizing an FESEM.

The procedure used for depositing the HA nanocrystals 880 on the surfaceof the implant 875 was similar to the procedure used in Example 11.However, the immersion time used in FIG. 13 b was approximately 60minutes. Thus, the immersion time is higher than that of Example 11.Accordingly, the amount of HA nanocrystals 880 deposited on the surfaceof the implant 875 is generally greater than that of Example 11.

EXAMPLE 13

FIG. 13 c is a scanning electron microscope image showing HAnanocrystals 902 after being deposited on the surface of a titanium6AL-4V ELI alloy implant 900. The image of FIG. 13 c was taken at 30 kXutilizing an FESEM.

The procedure used for depositing the HA nanocrystals 902 on the surfaceof the implant 900 was similar to the procedure used in Example 9.However, the immersion time used in FIG. 13 c was approximately 240minutes. Thus, the immersion time is considerably higher than that ofExamples 11 and 12. Accordingly, the amount of HA nanocrystals 902deposited on the surface of the implant 900 is generally greater thanthose of Examples 11 and 12.

Laboratory Testing On Animals

An animal study was conducted to test the performance of severalimplants having HA nanocrystals deposited thereon. The study utilized abone-to-implant tensile strength test comparing the results of twocontrol groups and six test groups. The control groups includedOsseotite® etched titanium alloy (6AL-4V ELI) implants and commerciallypure (CP) titanium implants. Three of the test groups includedOsseotite® etched CP titanium implants with HA nanocrystals depositedthereon. The remaining three test groups included Osseotite® etchedtitanium alloy (6AL-4V ELI) implants with HA nanocrystals depositedthereon. The test groups differed in the level of coverage (light,medium, and heavy) of the HA nanocrystals on the respective implants.Twelve implants were tested for each of the six test groups and twocontrol groups.

CP titanium implants like the implants 775, 800, 825 shown in FIGS. 12a-c and described in Examples 8, 9, and 10 above were also among theimplants tested during the study. Implants made pursuant to Example 8(FIG. 12 a) were among the group of Osseotite® CP titanium implantshaving light coverage. Implants made pursuant to Example 9 (FIG. 12 b)were among the group of Osseotite® CP titanium implants having mediumcoverage. Implants made pursuant to Example 10 (FIG. 12 c) were amongthe group of Osseotite® CP titanium implants having heavy coverage.

Titanium alloy implants like the implants 850, 875, 900 shown in FIGS.13 a-c and described in Examples 11, 12, and 13 above were among theimplants tested during the study. Implants made pursuant to Example 11(FIG. 13 a) were among the group of Osseotite® titanium 6AL-4V ELIimplants having light coverage. Implants made pursuant to Example 12(FIG. 13 b) were among the group of Osseotite® titanium 6AL-4V ELIimplants having medium coverage. Implants made pursuant to Example 13(FIG. 13 c) was among the group of Osseotite® titanium 6AL-4V ELIimplants having heavy coverage.

The tensile strength test study was conducted utilizing rats as the testsubjects. The implants were surgically implanted into both femurs of thetest subjects in a bi-cortical manner. The implantation site was thenclosed and allowed to heal for nine days, after which the test subjectswere sacrificed. The subject femurs were then removed, and thebone/implant cross sections were prepped for the tensile strengthtesting. Wires were then inserted through the medullary cavity on bothsides of the implant. The implants were subsequently fixed on anInstron® Universal Testing System, manufactured by Instron Corporation®(Burlington, Ontario). The wire was pulled vertically with increasingforce until the bone broke away from the implant. The maximum amount offorce before breakage was measured in Newtons. The implant was thenturned 180 degrees, and the test was repeated on the other side of theimplant. Thus, two tests were available for each implant.

The results of the testing indicated statistically significantdifferences (95% confidence level) between the mean values of thecontrol groups and each of the corresponding test groups. The meanvalues of each of the Osseotite® titanium alloy 6AL-4V ELI implants testgroups (light, medium, and heavy coverage) required 10.8N (n=23,standard deviation=5.32), 14.1N (n=24, standard deviation=5.98), and12.8N (n=23, standard deviation=4.78) of force, respectively, to breakaway the bone from the implant. The mean values of the Osseotite® CPtitanium test groups (light, medium, heavy coverage) required 8.2N(n=24, standard deviation=4.21), 10.5N (n=24, standard deviation=4.38),and 11.6N (n=24, standard deviation=4.89) more force, respectively, tobreak away the bone from the implant. The mean values of each of theOsseotite® titanium alloy 6AL-4V ELI implants test groups (light,medium, and heavy coverage) required 157%, 235%, and 204% more force,respectively, to break away the bone from the implant than that of thecorresponding control group. The mean values of the Osseotite® CPtitanium test groups (light, medium, heavy coverage) required 901%,1178%, and 1319% more force, respectively, to break away the bone fromthe implant than the corresponding control group. Thus, any amount of HAnanocrystal coverage (i.e., light, medium, and heavy) was shown to bebeneficial to the performance of the implants, and the implants havingmedium and heavy HA nanocrystal depositions were found to have slightlybetter performance than those having light deposition.

Initial Results Of Clinical Testing On Humans

A human study was conducted to compare the performance of implantshaving HA nanocrystals deposited thereon to those not having HAnanocrystals deposited thereon. All of the implants used in the studywere custom made 2mm×10mm Osseotite® titanium alloy 6AL-4V ELI siteevaluation implants (SEI), which included a roughened etched surface asdefined above. The control group included sixteen SEI with no furthertreatment (Control-SEI). The test group included sixteen SEI withdiscrete HA nanocrystals deposited on the roughened surface (Test-SEI).

The protocol used during the clinical testing was approved by the EthicCommittee of the University of Chieti-Pescara, and all patients providedwritten informed consent. To ensure balance and to minimize differencesin bone density and patient biology, one Control-SEI and one Test-SEIwere placed in each of fifteen patients. One of the fifteen patientsreceived an additional Control-SEI and Test-SEI for a total of four SEI(Patient No. 11 of Table 1). The SEI were placed, using a randomizationscheme, either in close proximity to each other on the same side of theposterior maxilla or in contralateral sites. After 8±1 weeks of healing,a guide post was attached to each of the SEI, and the SEI were removedusing a trephine with an internal diameter of 4 mm. The SEI were thenevaluated under light microscopy and confocal laser scanning microscopy(CLSM).

Significant differences were observed between the Control-SEI and theTest-SEI. For example, histologic observations in the Control-SEI showedformation of new bone around the implant surface that was not always indirect contact with the entire perimeter of the threads of the implant.The newly formed bone in the Test-SEI, on the other hand, was in tightcontact with the implant surface and adapted completely to themicro-irregularities of the implant surface.

Histomorphometric analysis of bone-to-implant (BIC) contact wasperformed on each of the Control-SEI and Test-SEI. The results of theanalysis are summarized in Table 1 below. TABLE 1 % BIC % BIC PatientNo. (Control Group) (Test Group)  1 4.3 45.1  2 54.1 0  3 40.0 52.0  424.0 65.1  5 3.0 23.0  6 15.3 22.4  7 30.3 15.0  8 19.6 47.7  9 8.1 53.110 7.2 47.0 11 (case 1) 9.8 19.0 11 (case 2) 19.8 13.5 12 53.1 22.0 1313.0 7.1 14 18.1 19.0 15 0 16.3 Summary (excluding patients with “0”values) N 14 14 Mean 19.0 32.2 Std. Dev. 14.18 18.49 Minimum 3.0 7.1Maximum 53.1 65.1

As shown in Table 1, the initial results of the testing indicatedstatistically significant differences between the mean BIC values of theControl-SEI and the TEST-SEI. Possible cutting artifacts were suspectedin one Control-SEI (Patient No. 15) and one Test-SEI (Patient No. 2),both of which were removed without any surrounding bone (BIC=0).Excluding these patients, the mean BIC value for the control-SEI was19.0 (n=14, standard deviation=14.18) and the mean BIC value for theTest-SEI was 32.2 (n=14, standard deviation=18.49). Thus, the TEST-SEIhaving discrete HA nanocrystals deposited thereon were found to performsubstantially better than the Control-SEI.

According to the methods of the present invention, the nanoparticles ofcalcium phosphate directly bond to a titanium oxide and/or titaniumhydroxide layer formed on the surface of the implant. Thus, one of thebenefits of the present invention is that it does not require anintermediary molecule (e.g., an alkoxide or tri-functional silanes suchas aminopropyltriethoxysilane) to bond the nanoparticles to the implant.Rather, the nanoparticles are deposited using a one-step process ofexposing the roughened surface of the implant to a colloidal solutionincluding the nanoparticles.

While the present invention has been generally described relative to thepart of the implant contacting bone tissue, it is contemplated that theacts etching, acid etching, roughening, and depositing herein describedmay be performed on the entire implant.

While the present invention has been described with reference to one ormore particular embodiments, those skilled in the art will recognizethat many changes may be made thereto without departing from the spiritand scope of the present invention. Each of these embodiments andobvious variations thereof is contemplated as falling within the spiritand scope of the claimed invention, which is set forth in the followingclaims.

1. A method of forming a nanocrystalline surface on an implant, themethod comprising the acts of: roughening at least a portion of theimplant surface to form a roughened surface; without forming an alkoxideon the roughened surface, depositing nanocrystals on the roughenedsurface, the nanocrystals comprising a material having a property thatpromotes osseointegration.
 2. The method of claim 1, wherein the implantis made of a metal selected from the group consisting of tantalum,cobalt, chromium, titanium, stainless steel, or alloys thereof.
 3. Themethod of claim 1, wherein the metal comprises titanium.
 4. The methodof claim 1, wherein the implant is made of a material including ceramic.5. The method of claim 1, wherein the implant is a dental implant. 6.The method of claim 5, wherein the portion of the implant surface is athreaded bottom portion for facilitating bonding with bone.
 7. Themethod of claim 1, wherein the act of roughening the implant surfacecomprises: removing a native oxide layer from the implant surface; andacid etching the resulting surface.
 8. The method of claim 1, whereinthe act of roughening the implant surface creates irregularities, theirregularities having peak-to-valley heights not greater than about 20microns.
 9. The method of claim 1, wherein the nanocrystals includehydroxyapatite, the nanocrystals being on the order of about 20nanometers to about 100 nanometers.
 10. The method of claim 9, whereinthe act of depositing the hydroxyapatite nanocrystals further includesusing a solution of 2-methoxyethanol solvent and the hydroxyapatitenanocrystals.
 11. The method of claim 10, wherein the act of depositingthe hydroxyapatite nanocrystals further comprises adjusting the pH ofthe solution.
 12. The method of claim 11, wherein the adjusting the pHof the solution includes using ammonium hydroxide.
 13. The method ofclaim 11, wherein the pH is adjusted to between about 9 and about 11.14. The method of claim 1 further comprising the act of rinsing theimplant in reverse osmosis/deionized water.
 15. The method of claim 14further comprising thermally curing the implant to sinter the depositedhydroxyapatite nanocrystals.
 16. The method of claim 14 furthercomprising the acts of: rinsing the implant in deionized water; anddrying the implant.
 17. The method of claim 14, wherein prior todepositing the hydroxyapatite nanocrystals, the method comprises rinsingthe implant in deionized water.
 18. A dental implant comprising: a headportion having a non-rotational feature; a lowermost end opposing thehead portion; and a threaded bottom portion for engaging bone betweenthe head portion and the lowermost end, the threaded bottom portionhaving a roughened surface with a substantially uniform array ofmicroscale irregularities having peak-to-valley heights not greater thanabout 20 microns, the threaded bottom portion further including discretenanoparticles located on the roughened surface, the nanoparticlesincluding hydroxyapatite nanocrystals.
 19. The implant of claim 18,wherein the implant is made of a metal selected from the groupconsisting of titanium and titanium alloys.
 20. The implant of claim 18,wherein the implant is made of a material including ceramic.
 21. Theimplant of claim 18, wherein the hydroxyapatite nanocrystals are on theorder of about 20 nanometers to about 100 nanometers.
 22. The implant ofclaim 18, wherein the roughened surface that receives the discretenanoparticles does not include an alkoxide or a tri-functional silane.23. A method of forming a nanocrystalline surface on an implant, themethod comprising the acts of: providing a metal substrate; immersing atleast a portion of the substrate in a colloidal solution having atemperature ranging from about 18° C. to about 32° C. for about 11.5minutes to about 240 minutes, the colloidal solution comprising: a2-methoxyethanol solvent, and a plurality of hydroxyapatite nanocrystalshaving a concentration ranging from about 0.01 weight percent to about 1weight percent relative to the overall solution; and adjusting the pH ofthe colloidal solution to about 9 to about 11.